There has been known a gas sensor which is attached to an exhaust passage of an internal combustion engine, such as an automotive engine, and which includes a detection element whose output changes in accordance with the concentration of a specific gas (for example, NOx (nitrogen oxides) or oxygen) within exhaust gas. The detection element includes at least one cell composed of a solid electrolyte member and a pair of electrodes provided thereon, and the output of the detection element (current flowing through the cell or electromotive force generated by the cell) changes in accordance with the concentration of the specific gas. This detection element has, at its front end, a detection portion whose output changes in accordance with the concentration of the specific gas. The circumference of a trunk portion of the detection element is surrounded by a metallic shell which is adapted to attach the gas sensor to an exhaust pipe, and the detection element is gas-tightly held by a sealing filler, such as talc, boron nitride, or glass, provided within the metallic shell. A rear end portion of the detection element projects rearward from the metallic shell, and is surrounded by a sheath attached to a rear end portion of the metallic shell. An elastic member formed of rubber is fitted into a rear end portion of the sheath, whereby the interior of the sheath is sealed.
In order to take out the output from the detection portion located at the front end, a plurality of output take-out portions are provided on the rear end portion of the detection element (for example, electrode pads are formed on the surface of the rear end portion of the detection element). A plurality of lead wires for electrically connecting the detection element and an external circuit are passed through the elastic member, and conduction members (metallic terminals) provided at the ends of the lead wires are connected to the output take-out portions (electrode pads). Moreover, a separator formed of an electrically insulating ceramic is disposed inside the sheath. The conduction members are accommodated in the separator such that they do not have contact with one another (for example, see Patent Document 1). Also, this separator secures insulation between the conduction members and the sheath.